1) The factors influencing T delta induction in mice and humans and the possibility that IgD may be used to augment antibody production in aged mice, perhaps in combination with IL-2. Memory B cell development and its T cell regulation in aged and young mice will be compared (Drs. G.J. Thorbecke and R.F. Coico). 2) The surface properties, numbers and functional activity of Langerhans cells in the skin of aged and young mice and humans, and the upregulation of surface antigen expression (particularly Ia antigen) on these cells by lymphokines. The Ia expression on these antigen-presenting cells in the epidermis is greatly impaired with age and this may influence the balance of the helper to suppressor T cell in responses to antigen presented via skin and in the response to skin tumors (Drs. D.V. Belsito and G.J. Thobecke). 3) The functional activity and interrelation between various T cell subsets in the immune response of aged mice as related to cell surface properties. Further characterization of three different types of suppressor cells and enumeration of suppressor cell precursors (Dr. S.R.S. Gottesman). 4) The regenerative activity of prethymic cells in aged mice and the heterogeneity of these cells in terms of their surface receptors. Assessment of the ability of the thymus in aged mice to receive and propagate immigrant prothymocytes (Dr. R. Basch). 5) The chemotactic response, endothelial cell adherence, and generation of bactericidal oxygen metabolites by granulocytes from aged humans, as well as the influence of lymphokines an adenosine on these responses as related to cell membrane and cytoskeleton properties (Drs. B. Cronstein and R. Hirschhorn).